The present invention relates to a wet type friction clutch and an electromagnetic clutch for use in a coupling device or a differential gear device of a vehicle.
Japanese Patent Provisional Publication No. 10-329562 discloses a torque transmitting device 301 which is exemplarily shown in FIG. 1.
The torque transmitting device 301 is comprised of a rotary case 303, an inner shaft 305, a main clutch 307, a ball cam 309, a pressure plate 311, a cam ring 313, a pilot clutch 315, an armature 317 and an electromagnet 319.
The torque transmitting device 301 is disposed between separate rear propeller shaft components which are rendered to be separate from one another during a two wheel drive condition in a four wheel drive vehicle, with the rotary case 303 being connected to a front side propeller shaft component while the inner shaft 305 is connected to a rear side propeller shaft component.
The rotary case 303 is comprised of a cylindrical member 321, to which the main clutch 307 is coupled, and a rotor 323 which forms a part of a magnetic flux path of the electromagnet 319, with the cylindrical member 321 being made of stainless steel to preclude a magnetic flux from being leaked from the magnetic flux path.
The main clutch 307 includes a multi plate clutch disposed between the cylindrical member 321 and the inner shaft 305, and the ball cam 309 is disposed between the pressure plate 311, which is connected to the inner shaft 305 for free movement, and the cam ring 313.
The pilot clutch 315 includes a multi plate clutch and is kept between the armature 317 and the rotor 323.
The torque transmitting device 301 is arranged such that the magnetic flux path of the electromagnet 319 is defined as indicated by a magnetic flux path 325 with the clutch rotor 323, the pilot clutch 315 and the armature 317 whereby, when the electromagnet 319 is energized, the armature 317 is attracted with the magnetic flux path 325 to cause the pilot clutch 315 to be pressured contact into a coupled condition.
Upon coupling of the pilot clutch 315, a pilot torque is produced to allow a drive power output of an engine to be imparted to the ball cam 309 to create a cam thrust force by which the main clutch 307 is urged to cause the torque transmitting device 301 to be coupled to transfer the drive power output to the rear wheel side to render the vehicle to be operative in the four wheel drive condition.
Further, if the excitation of the electromagnet 319 is interrupted, the pilot clutch 315 is released to cause the ball cam 309 to lose the cam thrust force whereby the main clutch 307 is released to uncouple the torque transmitting device 301 for disconnecting the rear wheel side to render the vehicle operative in the two wheel drive condition.
The pilot clutch 315 including the multi plate clutch is comprised of a plurality of outer plates and a plurality of inner plates, which are alternately interleaved with respect to one another. Further, the outer plates are disposed in engagement with the cylindrical member 321 and, to this end, an outer periphery of each outer plate is formed with engaging protrusions circumferentially spaced in a given distance. The inner plates are disposed in engagement with the cam ring 313 and, to this end, an inner periphery of each inner plate is formed with engaging protrusions circumferentially spaced in a given distance.
The pilot clutch 315 is arranged to be coupled when the interleaved outer plates and the inner plates are brought into pressured contact with respect to one another to create a frictional force due to the magnetic flux path 325 of the electromagnet 319 to cause the armature 317 to be attracted. In contrast, during an uncoupled condition of the pilot clutch 315, since the outer plates and the inner plates are operative for free sliding movements, there is a need for these components to be lubricated with oil and, for such a purpose, the rotary case 303 is filled with oil.
With the pilot clutch 315, since the outer plates and the inner plates are sliding under interleaved conditions even during the two wheel drive condition where the electromagnet 319 is de-energized, there is a probability for a drag torque to be created between the adjacent clutch plates due to the viscosity of oil at a low operating temperature. As the drag torque exceeds a given level, the outer plates and the inner plates tend to operate just as they are coupled, inviting a risk for the pilot clutch 315 to produce the pilot torque which is transferred through the ball cam 309 to the main clutch 307 which is consequently exerted with an urging force to transfer the drive power output to the rear wheel side.
During a time interval in which the coupling of the clutch is not required, if the drive power output is transferred to the rear wheel side, the vehicle encounters a drive power loss with a resultant adverse affect in a running characteristic or fuel consumption of the vehicle.
Further, while the magnetic flux produced by the electromagnet 319 forms the magnetic flux path 325 through which the magnetic flux path is circulated via the clutch rotor 323, the pilot clutch 315 and the armature 317 set forth above, the inner clutch plates of the pilot clutch 315 are arranged to be formed with through-bores to preclude a reduction in the magnetic flux density caused by the leakage of the magnetic flux from the circulated magnetic flux path 325.
The above described inner clutch plate is formed with a plurality of the through-bores between which a bridge portion is intervened. Outer clutch plates, which are not shown, are formed with through-bores with a similar structure. With such a structure, an inner peripheral portion and an outer peripheral portion of each through-bore form magnetic flux path forming portions which serve as routes of the circulated magnetic flux path 325.
However, even in a case where the clutch plate of such a state-of-the-art electromagnet clutch is formed with the circumferentially extending through-bores in an area between the inner peripheral, magnetic flux path forming portion and the outer peripheral, magnetic flux path forming portion, the clutch plate is inevitably formed with the above described bridge portions on a circumferential periphery at six locations thereof for interconnecting the inner peripheral portion and the outer peripheral portion, with associated opposing walls of the above described bridge portions of the mutually adjacent clutch plates bearing in contact with one another.
As a result, the associated opposing walls, held in contact with respect to one another, of the bridge portions become loopholes through which the magnetic flux circulating in the magnetic flux path forming portion escapes to an opposing magnetic flux path, resulting in a reduction in the magnetic flux density produced by the electromagnet 319 to decrease the attraction force to be exerted to the armature 317 for thereby causing the coupling force of the pilot clutch mechanism to be lessened.
In order for the amount of escape of the magnetic flux to be decreased, further, it is conceivable to reduce the number of the above described bridge portions, but the clutch plate undergoes a decreased strength with a deterioration in the durability.
It is, therefore, an object of the present invention to provide a wet type friction clutch and an electromagnetic clutch which have an ability of eliminating a drag torque between clutch plates with no undesired coupling of the clutch plates whereby, when applied to a torque transmitting device (coupling device) of a vehicle, the vehicle has an improved fuel consumption with no adverse effect to a running characteristic.
It is another object of the present invention to provide a clutch plate for an electromagnetic clutch which includes a bridge portion with a reduced whole surface area, while ensuring a strength required for the bridge portion intervening between through-bores, for decreasing the amount of escape of a magnetic flux to provide an improved attracting force of an electromagnet.
According to one aspect of the present invention, there is provided a wet type friction clutch operatively disposed between first and second torque transmission components, which comprises a first plurality of clutch plates disposed for rotation with the first torque transmission components, a second plurality of clutch plates interleaved with the first plurality of clutch discs and disposed for rotation with the second torque transmission component, a clutch operator operative to selectively render the first and second plurality of clutch plates to engage or disengage, and an oil guide passageway formed on at least one of adjacent clutch plates to introduce an oil to sliding areas of the adjacent clutch plates and extending in a given length along circumferential peripheries of the adjacent clutch plates to communicate with an oil chamber to allow the oil to be introduced into the sliding areas of the adjacent clutch plates.
The clutch plates are lubricated with the oil retained in the oil guide passageway formed in at least one of the adjacent clutch plates.
According to the present invention, since the oil guide passageway formed in at least one of the adjacent clutch plates communicates with the oil chamber, rotation of the clutch plate allows the oil to be introduced to the oil guide passageway due to a xe2x80x9cWeissenberg Effectxe2x80x9d to cause the oil to be guided to sliding areas of the adjacent clutch plates for thereby compelling the adjacent clutch plates to be smoothly separated from one another with the oil which is introduced thereto. This results in an effective elimination of the drag torque between the clutch plates.
Accordingly, in a case where the wet type friction clutch of the present invention is applied to a pilot clutch of a coupling device or a differential gear device of a vehicle, there is no probability for the vehicle to inadvertently encounter a four wheel drive condition, resulting in a stabilized running characteristic with no loss in drive power output to improve fuel consumption.
According to another aspect of the present invention, there is provided a wet type friction clutch operatively disposed between first and second torque transmission components, which comprises a first plurality of clutch plates disposed for rotation with the first torque transmission components, a second plurality of clutch plates interleaved with the first plurality of clutch discs and disposed for rotation with the second torque transmission component, a clutch operator operative to selectively render the first and second plurality of clutch plates to engage or disengage, a first oil guide passageway formed on at least one of adjacent clutch plates to introduce an oil into sliding areas of the adjacent clutch plates, and a second oil guide passageway formed on the other one of the adjacent clutch plates, wherein the first oil guide passageway is formed to have a volume different from that of the second oil guide passageway to allow the oil to be introduced into the sliding areas of the adjacent clutch plates from the first and second oil guide passageways.
According to another aspect of the present invention, there is provided a clutch plate for an electromagnetic clutch having a group of clutch plates including first clutch plates disposed for rotation with a drive shaft and second clutch plates interleaved with the first clutch plates and disposed for rotation with a driven shaft, an electromagnet disposed at one side of the group of clutch plates, and an armature disposed at the other side of the group of clutch plates to be retracted by an electromagnetic force generated by the electromagnet for thereby causing the group of clutch plates to be brought into pressured contact such that the clutch plates are coupled, wherein the clutch plate has a plurality of through-bores, formed along a circumferential periphery of the clutch plate in alignment with a magnetic flux path forming portion which establishes a magnetic flux path generated by the electromagnet, between which a bridge portion is intervened for interconnecting an inner circumferential periphery and an outer circumferential periphery of the clutch plate. The clutch plate comprises a body formed with oil guide passageways, composed of the through-bores, and the bridge portions, each of which includes opposing walls facing opposed clutch plates, respectively, and an inner wall facing each of the through-bores, wherein each of the bridge portions is formed such that, while ensuring a given cross sectional area, a circumferentially peripheral length of the opposing wall is shorter than that of each bridge portion.
With such a structure, the bridge portion has a given cross sectional area for thereby providing a strength required for interconnecting the inner peripheral portion and the outer peripheral portion of the clutch plate, with the opposing walls of the bridge portion having the circumferentially peripheral length configured to be shorter than the circumferentially peripheral portion of the bridge portion such that the cross sectional shape of the bridge portion has a reduced wall thickness portion extending toward the inner wall from at least one circumferentially peripheral end portion of the opposing wall.
Accordingly, with such a bridge portion, since the contact surface areas of the opposing walls of the bridge portions of the mutually adjacent clutch plates are decreased, it is possible to reduce the amount of leakage of the magnetic flux passing through the bridge portions.
According to another aspect of the present invention, there is provided a clutch plate for an electromagnetic clutch having a group of clutch plates including first clutch plates disposed for rotation with a drive shaft and second clutch plates interleaved with the first clutch plates and disposed for rotation with a driven shaft, an electromagnetic coil disposed at one side of the group of clutch plates, and an armature disposed at the other side of the group of clutch plates to be retracted by an electromagnetic force generated by the electromagnetic coil for thereby causing the group of clutch plates to be brought into pressured contact such that the clutch plates are coupled, wherein the clutch plate has a plurality of through-bores, formed along a circumferential periphery of the clutch plate in alignment with a magnetic flux path forming portion which establishes a magnetic flux path generated by the electromagnetic coil, between which a bridge portion is intervened for interconnecting an inner circumferential periphery and an outer circumferential periphery of the clutch plate. The clutch plate comprises a body formed with oil guide passageways, composed of the through-bores, and the bridge portions each of which includes opposing walls facing opposed clutch plates, respectively, and an inner wall facing each of the through-bores, wherein each of the bridge portions is formed such that, while ensuring a given cross sectional area, each bridge portion is smaller in thickness than the magnetic flux path forming portion.
With such a structure, the bridge portion has a given cross sectional area for thereby providing a required strength, with the thickness of the bridge portion being designed to be smaller than that of the magnetic flux path forming portion to provide no probability of contact between the opposing walls of the associated bridge portions of the mutually adjacent clutch plates for enabling elimination of the amount of leakage of the magnetic flux via the associated bridge portions.